1. Field of the Invention
This invention relates to novel, carbamylbiuret-modified polyisocyanates which are useful for preparing urethane-based microcellular foams and elastomers having excellent physical properties.
2. Description of the Prior Art
Urethane-based microcellular foams and elastomers are widely used in industry. Thus, these foams and elastomers are used to prepare exterior automobile parts, coatings, and adhesives.
Many biuret polyisocyanates are known to those skilled in the art. These biuret polyisocyanates may be prepared by reacting an organic diisocyanate with water (U.S. Pat. Nos. 3,124,605 and 3,903,127), formic acid (U.S. Pat. No. 3,350,438), tertiary alcohols (U.S. Pat. No. 3,358,010), monoamines (U.S. Pat. No. 3,392,183), diamines (U.S. Pat. Nos. 3,441,588 and 3,903,126), ureas (U.S. Pat. No. 3,367,956 and U.K. Patent Specification No. 1,043,674), and other biuretizing agents (U.S. Pat. No. 3,903,127).
Biuret polyisocyanates react with compounds bearing active hydrogen to form polyurethanes; see, e.g., U.S. Pat. No. 3,201,372.
German Pat. No. 883,504 discloses a reaction between ureas and isocyanates to prepare a reaction mixture having a high isocyanate content. According to U.S. Pat. No. 3,367,956, the process of the German patent results only in a high molecular weight condensation product.
Ureas are disclosed to react with diisocyanates by Angewandte Chemie 72 (1960), page 1002.
U.S. Pat. No. 3,367,956 discloses a process for the preparation of biuret polyisocyanates wherein an organic polyisocyanate is reacted with a substituted urea at a temperature of from about 150 to about 250 degrees Centigrade. It is believed that the process of this patent proceeds in accordance with the following reaction: ##STR2##
German Offen. No. 2,329,300 discloses a process for the preparation of iminoimidazolidinedions-modified polyisocyanate wherein diisocyanate is reacted with hydrocyanic acid and an organic tertiary amine catalyst.
U.S. Pat. No. 3,775,427 discloses a process for the preparation of polyisocyanates which contain hydantoin groups wherein a polyisocyanate is reacted with a .alpha.,.omega.-bis(hydantoinyl)alkane. The products of this patent are either viscous liquids or solids. They are unsuitable for use in urethane elastomeric microcellular foams for several reasons. In the first place, their structure contains a relatively long, flexible alkyl (or other type) bridge connecting the two hydantoin rings, thereby causing a less effective phase separation of hard and soft segments in the resulting final product and resulting in an impairment of the physical properties of the elastomer made from this product. In the second place, the physical states of these compounds and their low --NCO contents render their use in microcellular systems impractical.